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SBI3U Content Test Review > Meiosis > Flashcards

Meiosis Flashcards

1
Q

What happens during asexual reproduction?

A

Offspring have the same chromosomes as parents and are genetically-identical

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2
Q

What happens during sexual reproduction?

A

There are differences between parent and offspring chromosomes which creates genetic diversity.

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3
Q

What is fertilization? What does it do?

A

The union of gametes; It doubles chromosome number – so to prevent chromosome number from doubling each generation, sex cells must be haploid.

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4
Q

What does meiosis enable?

A

The sexual life cycle of eukaryotes by producing such haploid cells.

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5
Q

What is meiosis?

A

A reduction division of the nucleus to form haploid gametes.

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6
Q

What does the process of meiosis do? (It divides)

A

It divides one diploid eukaryotic nucleus to form four haploid nuclei

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7
Q

How many times is the original diploid cell divided in this process?

A

It divided twice in this process – Meiosis I and Meiosis II

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8
Q

Since the chromosome number is halves, what is meiosis called?

A

A reduction division

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9
Q

What are somatic cells? Are they haploid or diploid?

A
  • ‘Body’ Cells
  • Diploid (2n)
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10
Q

What are sex cells? Are they haploid or diploid?

A

-Gametes (egg/sperm)
-Haploid (n)

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11
Q

What are gametes?

A

-Males: Sperm are produced in the male gonads called the testes.
- Females: Ova (Ovum = si.) are produced in the female gonads called the ovaries.

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12
Q

What happens during fertilization? What is the result called?

A
  • During ovulation, an ovum is released from the ovary and transported to an area where fertilization can occur.
    -The result is called a zygote
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13
Q

What is the process of fertilization?

A

Sperm + Ovum (egg) (arrow-fertilization) Zygote

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14
Q

What are homologous chromosomes?

A

Chromosomes of the same size and structure, with the same sequence of genes (i.e. same genes at the same gene loci)

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15
Q

Although homologous chromosomes have the same genes, what might they have that is different?

A

Different alleles for the gene.

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16
Q

In humans, how do homologous chromosomes exist?

A

In humans, one of each chromosome type comes from the mother and one of each type comes from the father to make 22-23 homologous pairs

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17
Q

What is technically not homologous?

A

Since males have one X and one Y chromosome as their 23rd pair, it is technically not homologous.

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18
Q

What do homologous chromosomes have? (in terms of alleles)

A

Alleles for the same genes at specific loci

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19
Q

What do sister chromatids of duplicated chromosomes have?

A

Same alleles for each gene.

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20
Q

What do homologous chromosomes have?

A

The same structure?

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21
Q

Are somatic cell nuclei (body cells) haploid or diploid

A

Diploid (2n)

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22
Q

What do somatic cell nuclei contain?

A

A homologous pair of each chromosome-one of the pair is paternal, inherited from the father, and the other is maternal, inherited from the mother.

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23
Q

Homologous chromosomes have the same what? (everything)

A

Same size and structure, and carry the same genes at the same loci.

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24
Q

What varies in homologous chromosomes?

A

The alleles carried at each locus

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25
22 of the human chromosome pairs are what? The other pair, the sex chromosomes, are what?
Homologous; Non-homologous
26
In humans, what set number of chromosomes determine gender?
The 23rd set
27
Describe the X Chromosome
Large with a centromere in the middle (2000+ genes)
28
Describe the Y Chromosome
Small with a centromere near the top (less than 100 genes)
29
What does the X chromosome carry?
Genes necessary to human development
30
What does the Y chromosome carry?
Genes needed for male development
31
What are the other 44 chromosomes in the human body called? What do they carry? What are their set numbers?
- Autosomes - They carry only non-sex-related genes - Homologous pairs 1-22
32
Show the process of Spermatogenesis
- Primary Spermatocyte (2n = 46) (arrow) - Meiosis I: - Secondary Spermatocyte (n = 23) - Secondary Spermatocyte (n=23); -Meiosis II: -Sperm (n) (n = 23) -Sperm (n) (n=23) -Sperm (n) (n=23) -Sperm (n) (n=23)
33
Summarize the process of Spermatogenesis in one point
4 sperm cells are produced from each primary spermatocyte
34
Show the process of Oogensis
-Primary Oocyte: Secondary Oocyte and Polar Body -Secondary Oocyte: Egg and Polar Bodies -Polar Body: More Polar Bodies
35
Summarize the process of oogenesis in one point
The polar bodies die...only one ovum (egg) is produced from each primary oocyte
36
What occurs during Interphase? (4 points)
- In the S-phase of the interphase before meiosis begins, DNA replication takes place. - Chromosomes are replicated and these copies are attached to each other at the centromere. - The attached chromosome and its copy are known as sister chromatids. - Following S-phase, further growth and preparation take place for meiosis.
37
What is the main event of Interphase?
-A homologous pair of chromosomes replicates during S-phase of interphase
38
What occurs during Prophase I? (4 points)
-Nuclear membrane dissolves -Centrioles migrate to the poles of the cell -Crossing-over between non-sister chromatids can take place. This results in recombination of alleles and is a a source of genetic variation in gametes. -The homologous chromosomes associate with each other to form bivalents (synapsis).
39
During prophase I, what happens to the homologous pair?
It associates during prophase I through synapsis, making a bivalent.
40
In prophase I, what takes place?(2 points)
- Crossing-over might take place between non-sister chromatids, leading to recombination of alleles. -The point of crossing-over between non-sister chromatid is called the chiasma (pl. chiasmata)
41
What does crossing-over do?
Increases genetic variation through recombination of linked alleles.
42
What are the three main stages of crossing-over?
-Synapsis: Homologous chromsomes associate -Chiasma Formation: Neighbouring non-sister chromatids are cut at the same point. -Recombination: As a result, alleles are swapped between non-sister chromatids.
43
What does crossing-over lead to?
Crossing over leads to more variation in gametes.
44
What occurs during Metaphase I? (3 points)
- Random orientation occurs - each bivalent aligns independently and hence the daughter nuclei get a different mix of chromosomes. - This is a significant source of genetic variation: there are 2n possible orientations in metaphase I and II. - That is 223 in humans – or 8,388,068 different combinations in gametes!
45
How does variation occur in Metaphase I?
-Through Mendel's Law of Independent Assortment
46
What does Mendel's Law of Independent Assortment state?
The presence of an allele of one of the genes in a gamete has no influence over which allele of another gene is present.
47
What is the difference between Random Orientation and Independent Assortment in Metaphase I?
- Random Orientation refers to the behaviour of homologous pairs of chromosomes (metaphase I) or pairs of sister chromatids (metaphase II) in meiosis. - Independent assortment refers to the behaviour of alleles of unlinked genes as a result of gamete production (meiosis).
48
What stages of Meiosis does genetic variation occur?
-Prophase I -Metaphase I -Metaphase II
49
What genetic variation occurs in Prophase I?
- Crossing-over between non-sister chromatids results in recombination of alleles
50
What genetic variation occurs in Metaphase I and Metaphase II?
Random orientation of the homologous chromosomes means there are 2n possible orientations in metaphase I and II. That is 223 in humans – or 8,388,068 different combinations in gametes!
51
What occurs during Metaphase I? (3 points)
- Allele have a 50 percent chance of moving to a particular pole. - The direction in which one bivalent aligns does not affect the alignment of other bivalents. - Therefore different allele combinations should always be equally possible (if the gene loci are on different chromosomes – this does not hold for linked genes)
52
What occurs during Anaphase I? (3 points)
- Spindle Fibres contract - Homologous pairs are separated and pulled to opposite poles - This is reduction division
53
In anaphase I, what is separated but what remains attached? What is this called?
The homologous pair is separated; the sister chromatids remain attached; this is the reduction division
54
What occurs during Telophase I? (4 points)
- New nuclei form and the cytoplasm begins to divide by cytokinesis - The nuclei are no longer diploid - They each contain one pair of sister chromatids for each of the species’ chromosomes - If crossing over and recombination has occurred then the sister chromatids will not be exact copies
55
What occurs during Prophase II?
- The nuclei break down - No crossing over
56
What occurs during Metaphase II? (4 points)
- Pairs of sister chromatids align at the equator. - Spindle fibres form and attach at the centromeres - Random orientation again contributes to variation in the gametes, though not to such an extent as in metaphase I - This is because there is only a difference between chromatids where crossing over has taken place
57
What happens during Anaphase II? (3 points)
- Spindle fibres contract and the centromeres are broke - The pairs of sister chromatids are pulled to opposing poles - Non-disjunction here will lead to two gametes containing the wrong chromosome number
58
What occurs during Telophase II? (4 points)
- New haploid nuclei are formed - Cytokinesis begins, splitting the cells - The end result of meiosis is four haploid gamete cells - Fertilization of these haploid gametes will produce a diploid zygote
59
Meiosis is prone to what? What happens in some cases?
- Meiosis is prone to error. - In some cases, chromosomes fail to split properly in either Anaphase I or Anaphase II.
60
What is chromosomes failing to split properly in either Anaphase I or Anaphase II called?
Non-Disjunction
61
What does Non-Disjunction result in?
The result is the production of a gamete with an extra chromosome (Trisomy) or a missing chromosome (Monosomy)
62
What are incidences of Non-Disjunction strongly correlated with?
Maternal age
63
What can happen during Non-Disjunction?
- In anaphase, a chromosome or pair of sister chromatids can be pulled to the wrong pole. - Non-disjunction leads to changes in chromosome number.
64
When can non-disjunction occur?
In anaphase I or anaphase II
65
What does non-disjunction produce? (with regards to gametes)
Gametes with an abnormal number of chromosomes; fertilization adds the homologous chromosomes.
66
What does non-disjunction result in? (zygotes and somatic cells)
A zygote and somatic cells with a trisomy of one chromosome, which can be fatal or cause disorders.
67
What are some non-disjunction syndromes and what is the chromosome abnormality?
-Turner Syndrome: One X and no Y sex chromosome -Klinefelter Syndrome: Two X and one Y sex chromosome -Patau Syndrome: Trisomy of chromosome 13 -Edwards Syndrome: Trisomy of chromosome 18
68
What are two methods of Non-Disjunction Detection?
-Amniocentesis -Chorionic Villus Sampling
69
Where are the cells sampled from during Amniocentesis?
-Fetal cells are obtained from fluid in the amniotic sac where the fetus is held during the pregnancy.
70
How are cells obtained during Amniocentesis?
Ultrasound is used to guide a large needle through the abdomen into the amniotic sac?
71
What is the risk of miscarriage in Amniocentesis?
1%
72
Where are cells sampled from in Chorionic Villus Sampling?
Fetal cells obtained from the chorion-a part of the placenta.
73
How are cells obtained in Chorionic Villus Sampling?
A sampling tool enters through the vagina - can be done earlier in the pregnancy
74
What is the risk of miscarriage in Chorionic Villus Sampling?
2%
75
What is karyotyping?
A pre-natal test used to check for gender, and non-disjunction disorders.
76
How do you deduce sex from a karyotype?
XX = Female XY = Male
77
How do you deduce chromosomal abnormalities from karyotypes?
- Errors in Meiosis can lead to the formation of zygotes with abnormal chromosome numbers (In humans, this is any number that is not 46 – 44 Autosomes, 2 Sex chromosomes) - Trisomy: Having a third (extra) chromosome - Monosomy: Having only one chromosome
78
What does Down Syndrome result from?
Trisomy of the 21st chromosome
79
Describe Down Syndrome
- The most common genetic condition - Causes physical and mental development delays - 50-60 year life expectancy - ~6,000 babies each year in the U.S. (Risk is strongly correlated with maternal age)

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